Yabu with your instructions. I am fine. Other people however...
I have witnessed
Full shop scanned and then the bugger goes "just off to get the cash out" and then proceeds to walk to other side of store/outside to ATM - two occasions I've witnessed this.
People who require an assistant to scan for them - tis a wrong queue issue not a self check out prob
People who stand about after they've paid for their shopping - presumably because no nimble checkout person is already scanning the next item to remind them to leave
People who lean on the scales/bagging area causing it to malfunction
People who don't know what fruit/veg it is they have bought
Random filing of loose fruit and veg items by Tesco. Occasionally peppers are not to be found under 'P'... no, they are under 'R' for Red Pepper
Those are the real issues 
People who talk loudly to the machines
People who can't manage to pack into their own bag
The assistants who appear at my elbow to state the bleedin' obvious when I have just paused for breath but cannot be found when I have an "age restricted product" or the machine breaks down mid scan